The present invention relates to semiconductor laser diodes, and is particularly applicable to high power laser diodes with a ridge-type design.
In order to respond to demand for semiconductor laser diodes having higher output and effective coupling to an optical fiber, it is necessary to suppress the occurrence of spatial hole-burning which prevents uniform distribution of carriers in the laser.
One method for preventing spatial hole-burning is to increase the width of the active region of the laser diode to lower the optical density at the output facet. However, increasing the width of the active region width is likely to generate emissions at a higher-order modes, destabilizing the emission of laser rays. Thus, there is a trade-off between the suppression of the higher-order mode emission and the spatial hole-burning are in a strict trade-off relation with respect to the active region width.
One method of moderating the trade-off relation is introduction of a flared structure in the active region, which enables the enlargement of the width of the active region at the laser output facet where reduction of the optical density is desirable. Increasing the active region width increases of the surface area of the output facet to secondarily suppress the facet destruction increasing the reliability of the semiconductor laser diode.
However, in the conventional semiconductor laser diode having the flared structure, the stable and continuous emission in the fundamental mode is difficult to attain, and the product yield of the semiconductor laser diode which is able to maintain stable fundamental mode emission is low.
In one aspect of the present invention, a semiconductor laser diode including: a semiconductor substrate; a resonator structure including a first facet having a reflective coating, a second facet having an antireflective coating, and a propagation direction which extends from the first facet to the second facet; and an active region including a linear section extending from the first facet along the propagation direction of the resonator and having a width xe2x80x9cdxe2x80x9d which is substantially uniform along the propagation direction, and a flared section extending from the linear section toward the second facet, the flared section having a tapered width increasing toward the second facet, wherein the relation of d less than xcex0/{2xc2x7(2xc2x7n0xc2x7xcex94n)0.5} holds in which An is a difference between equivalent refractive indexes of the active region and inactive regions extending along both sides of the active region, xe2x80x9cdxe2x80x9d is a width of the linear section in the active region, xe2x80x9cxcex0xe2x80x9d is a laser emission wavelength, and xe2x80x9cn0xe2x80x9d is an equivalent refractive index of the linear, is provided.
In accordance with the present invention, the semiconductor laser diode can be realized which emits in a stable fundamental mode by satisfying the above relation for increasing the effect for suppressing the spatial hole-burning phenomenon.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.